12/16/2012 12:50 AM PST BY TMZ STAFF

The cash-poor Klein has listed the 3,500 sq. ft. property for $6.63 MILLION.And get this ... Klein tried to unload the property last year, listing it for a cool $12 mil.

Klein's fall has been breathtaking. He was once the premiere dermatologist in Bev Hills ... the dermatologist to the stars, including MJ, Elizabeth Taylor and Cher.

Klein's medical practices were put under a microscope after MJ died. The doc was fueling MJ with huge quantities of prescription drugs, including Demerol -- he injected MJ with Demerol 51 times in the 3 months preceding his death.